article: People usually check whether their keys, wallets and phones are with them before going out. But many people in China now have one more important thing to take, a face mask. They hope that it can protect them from polluted air.
  Since January 2013, many cities in China have seen a lot of foggy days. In Beijing, only five days in January _  . What's the difference between fog and smog?
  According to scientists, fog is made up of tiny   drops of water and also ice particles   during very cold conditions. Smog is dirty air that looks like a mixture of smoke and fog, caused mainly by smoke from cars and factories in cities.
  An official for the Ministry of Environmental Protection told Beijing News that PM2.5 pollution is the main problem with air pollution. PM 2.5 refers to pollution with small particles 2.5 micrometers or less in diameter  .
  According to the Chinese Academy of Sciences, two main factors that cause PM 2.5 are motor vehicles and the burning of coal.
  Poor air has done harm to people's health. Children and the elderly are more at risk. A report from Beijing Children's Hospital shows that from December 5 to December 11, 2013, half of the patients in the hospital came for respiratory   problems.
  Air problems and environmental protection have become a care for the whole nation.
  Premier Li Keqiang made his last Government Work Report  on March 6, 2014. The report said that the government should work hard to prevent pollution and give people a healthy living environment.
  It calls on people to make full use of energy and resources   and cut down on energy use.
  'We should give people hope through our actions,' Li said.
question: From Li Keqiang's report, we learn that   _  .
options: the environment has improved a lot since Li was in office many people have breathing problems because of the air pollution the air pollution problem is the government's task the government will try its best to solve the air pollution problem